1. Field of the Invention
The present invention relates to an information signal transmitting apparatus which is adaptable for connecting a variety of video equipment, for example, in conformity with IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 1394--High Performance Serial Interface Bus (referred to simply as IEEE 1394 hereinafter). The present invention simplifies the work necessary for installing a variety of equipment by transmitting and receiving information indicative of equipment attributes and equipment addresses between the equipment, and determining whether each equipment is connectable or not to a network based on the attribute information.
2. Description of the Related Art
When a variety of video equipment such as a TV tuner, a monitor device and an optical disk device are connected to construct an AV system, the system has been hitherto made up by, for example, connecting the variety of video equipment via specific lines with a display device, i.e., a final output device for the variety of video equipment, installed at the center.
In other words, where an AV system is constructed from those pieces of video equipment, video sources such as a TV tuner and an optical disk device are connected in any case so as to output video signals and audio signals to a monitor device as a final output object. Thus, a monitor device for use in that type of AV system has a plurality of video input terminals and audio input terminals to which are applied video signals and audio signals from the individual video sources.
Furthermore, for video equipment having a recording function such as an optical disk device, a video source such as a tuner is connected to the video equipment directly or via an external output terminal of a monitor device for applying video and audio signals to it. The connection between the video equipment and the video source is made by shielded wires or a coaxial cable through which the video and audio signals are transmitted while reducing possible mixing of noise etc.
On the other hand, in a video tape recorder having an integrally built-in camera wherein a video signal is processed in the form of a digital signal, video and audio signals can be input and output through an interface specified by IEEE 1394, for example.
IEEE 1394 specifies a low-cost standard serial interface with a high speed. A technical outline of IEEE 1394 is as follows.
&lt;Signal Transmission&gt;
According to IEEE 1394, a signal is transmitted using two sets of twisted pair wires. In signal transmission, the two sets of twisted pair wires are both employed to transmit a signal in one direction to establish the so-called half duplex communication. One wire transmits data and the other wire transmits a signal called a strobe. The reception side reproduces the clock by computing exclusive OR of the two signals.
Three types of data rate, i.e., 98.304 Mbps (S100), 196.608 Mbps (S200) and 393.216 Mbps (S400), are defined. Compatibility with the lower-order rates is employed so that the equipment having a higher rate can support the lower rate(s) as well.
&lt;Equipment Connection&gt;
Each equipment is able to have maximum 26 ports. By connecting equipment ports to each other, maximum 63 pieces of equipment can be interconnected. The interconnection is free to establish so long as there is no loop connection and the connecting stages do not exceed 16.
According to IEEE 1394, when a variety of equipment are connected, a bus initializing process is performed and a Tree structure is formed in which one piece of equipment is a root and other pieces of equipment are children or grandchildren of the root. Then, addresses are automatically allocated to the variety of equipment. IEEE 1394 has therefore a feature that the degree of freedom in method of connecting cables is large and the setting incidental to the cable connection is automated.
&lt;1394 Communication&gt;
According to IEEE 1394, a signal transmitted from one piece of equipment is relayed by another piece of equipment so that the same signal is transmitted to all pieces of equipment in the network. In other words, electrical connection is point-to-point, but a bus type network is formed from the logical point of view. It is therefore required to arbitrate bus usage rights before each equipment starts transmission.
To obtain the bus usage right, the equipment first waits for the bus becoming free, and then issues a request signal to its parent equipment. The equipment having received the request signal relays the request signal to its parent equipment, causing the request signal to finally reach the root. The root returns a permission signal upon receiving the request signal, and the equipment receiving the permission signal is allowed to start communication. When a plurality of equipment issue request signals at the same time, the request from one piece of equipment is allowed, but the requests from others are rejected.
&lt;Real-time Operation&gt;
In such a way, IEEE 1394 enables a plurality of equipment to share one bus in a time division multiplex manner through a struggle for the bus usage right. But when data requiring real-time operation, such as an audio signal and a video signal, is transmitted, it is necessary to guarantee the communication with certain time intervals and prevent omission of the data.
According to IEEE 1394, the so-called isochronous communication technique is used to transmit the data requiring real-time operation. The node managing the isochronous communication is selected during the bus initializing process, and the managing node allocates a necessary band to the equipment trying to transmit data with the isochronous communication. The root transmits a cycle start packet per 125 .mu.s, and the equipment having received the allocated band transmits an isochronous packet in succession to the cycle start packet.
The above technique ensures that the equipment having received the allocated band can always have an opportunity to transmit data per 125 .mu.s. If the total amount of bands used for the isochronous communication exceeds the bus capacity, allocation of the bands cannot be performed and the isochronous communication cannot start.
The interface of IEEE 1394 is expected in making a variety of video equipment more easily connected because it enables the variety of video equipment to share one bus in a time division multiplex manner and to make up a network in the ring or star form through interconnection between the equipment.
With the interface of IEEE 1394, however, between which ones of equipment video and audio signals are transmitted and received is managed by a host managing the operation of the entire system. Eventually, the cable connection between equipment can be simplified, but the connection relationship between equipment is required to be set in the host. Stated otherwise, although the work of connecting cables is itself simplified, there is a problem that the setting of the connection relationship between equipment is complicated and eventually the work of installing the variety of equipment is complicated.